1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, particularly to an electrophotographic photosensitive member having superior surface hardness and abrasion resistance. The present invention relates also to an electrophotographic apparatus, a device unit, and a facsimile machine employing that electrophotographic photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members are widely used mediums for image formation in the electrophotographic process such as a copying machine, a laser beam printer, and a facsimile machine. In a usual electrophotographic image forming process, the electrophotographic photosensitive member is repeatedly subjected to a cycle of electric charging, exposure to light, development of the image, transfer of the developed image, cleaning, and removal of the electric charge. In more detail, firstly an electrophotographic photosensitive member is electrostatically charged uniformly. The uniformly charged photosensitive member is imagewisely exposed to light by use of a halogen lamp, a laser beam, or the like to decay the charged potential at the light-exposed area, thus forming an electrostatic latent image. Then the electrostatic latent image is developed with a developing agent (i.e., a toner composed of charged fine particles) to form a visible image on the electrophotographic photosensitive member. The visible image is transferred onto an image receiving material by Coulomb's force caused by transfer charging and pressure application. In the image transfer, not all of the toner is transferred, but a portion of the toner remains on the electrophotographic photosensitive member. The remaining toner has to be removed by cleaning for repeated use of the photosensitive member. After the cleaning, the influence of the previous staticization is removed by intense light exposure, bias application or the like method to make the photosensitive member ready for the next process cycle.
The cleaning process is explained below in more detail. In the cleaning process, the fine particles such as toner particles are removed from the surface of a photosensitive member using a fur brush, a magnetic brush, a blade, OF the like means. In particular, blade cleaning is widely employed in recent years because of the high effectiveness of cleaning and the simple constitution of the cleaning device. The cleaning blade is constituted of a blade 1, namely a plate made of an elastic material like polyurethane, and a support 2 for holding the blade as shown in FIG. 1 to FIG. 4. The blade is pressed against the photosensitive member along the length direction of the photosensitive member. The blade may be brought into contact either in the direction following the rotation of the photosensitive member 3 as shown in FIG. 5 or in the direction counter to the rotation as shown in FIG. 6. The latter direction of the contact is preferred in view of the cleaning efficiency. Higher pressure of contact of the blade 1 to the photosensitive member 3 is preferable for further improvement of the cleaning efficiency.
The improvement of the cleaning efficiency is especially important in order to maintain the image quality in repeated use. However, a higher contact pressure results in the increase of frictional force between the photosensitive member and the blade, which causes abrasion and scratches of the photosensitive member, thus shortening the life of the photosensitive member.
On the other hand, organic photosensitive materials mainly used as the electrophotographic photosensitive member because of the advantages of high productivity, low cost, and non-pollution, have lower surface hardness than the ones employing an inorganic photoconductive material, and the surface is liable to be abraded and scraped by the cleaning blade.
To avoid such disadvantages, many attempts have been made to obtain a photosensitive layer having high hardness using polymerization of a monomer or an oligomer. For example, the attempts are disclosed in Japanese Laid-Open Patent Application Nos. 55-85058, 61-41152, 61-201461, 62-201460, 1-116553, 1-134364, 1-134365, and so forth.
However, the monomers, oligomers, and the polymerization products are sometimes not sufficiently compatible with or dispersible in photoconductive compounds, and the photoconductive compounds tend to deteriorate in the polymerization step.
To meet the recent needs for further higher image quality and higher durability, electrophotographic photosensitive members are being investigated which have higher mechanical strength.